Hydrophilic films have applications in a variety of fields. One of the methods to make hydrophilic films is to modify the substrate film with a hydrophilic coat layer. It was reported in prior art that a coat of nanometer silicon dioxide was applied on the substrate to improve hydrophilicity, and thereby to improve liquid flow rate and antifogging property. However, with regard to the hydrophilic films of the prior art, direction of liquid diffusion on a hydrophilic surface cannot be controlled; therefore, diffusion rates of the liquid in different directions are the same.
For applications in some fields, it is necessary for liquid to diffuse in a certain direction. For example, in modern medical diagnoses, it is necessary to use various types of analytical test strips. These test strips are used to test levels of glucose, cholesterol, protein and other substances in blood and urine. In order to monitor blood sugar level of a diabetic patient, it is necessary to use a blood glucose meter and test strips to conduct several tests every day. Since liquid flow on current test strips is not directional, a considerable amount of blood samples collected in the tests is not utilized. In order to increase utilization rate of the blood sample and to reduce the amount of blood used in each test, it is desired to make the blood sample flow rapidly in a certain direction on the test strips.
Thus, there is a need to develop a hydrophilic film that can cause liquid to diffuse rapidly in a certain direction.